T.O. 33B-1-16-76.2.2 BasicRequirementsforProductionofX-Rays.X-rays are produced when some form of matter is struck by a rapidly moving electron. To accomplish this, three basicrequirements must be met.6.2.2.1 SupplyOfElectrons.There must be a supply of the electrons. Fortunately, they can be supplied by simply raising the temperature of asuitable material. An electron source is readily obtainable in as much as all matter is generally considered to becomposed of electrons and other minute particles. All that is necessary is to sufficiently heat the proper material. Asthe temperature rises, the electrons become more and more agitated until finally they escape or "boil off” the material,surrounding it in the form of an electron cloud (see Figure 6-5). This is known as thermionic emission. In an X-raytube the heated material is known as the filament, which is similar to the filament in a light bulb. Just as in a light bulbthe filament is heated by passing electrical current through it.Figure 6-5. Electron Cloud.6.2.2.1.1This cloud of electrons simply hovers around and returns to the emitting substance unless some external action or forcepulls it away.6.2.2.2 MovementoftheElectrons.Movement of the emitted electrons is the second step in producing X-rays. This movement is brought about by therepelling and attracting forces inherent in electrical charges. The fundamental law of electrostatics states that likecharges repel each other and unlike charges attract each other. Electrons are negative charges, thus repel each other.However, a stronger attracting force is needed to accelerate the electrons to a higher velocity. Therefore, a strongopposite (positive) charge is used to move the electrons from one point to another. It is important that this movement isconducted in a good vacuum, otherwise the electrons collide with air molecules and lose energy through ionization andscattering. In an X-ray tube the anode is given a positive charge with respect to the filament, which is part of thecathode.
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